Divalent europium-activated barium-magnesium pyrosilicate

ABSTRACT

Divalent europium-activated BaMg2Si2O7 phosphors are useful in fluorescent lamps. The phosphors have spectral energy distribution curves which peak at 400 nanometers and which have a very narrow emission band.

United States Patent Barry Mar. 21, 1972 [54] DIVALENT EUROPIUM-ACTIVATED 3,260,675 7/1966 McAllister ..252/301.4 F BARIUM-MAGNESIUM PYROSILICATE 3,451,941 6/1969 McAllister ..252/301 .4 F [72] Inventor: Thomas L. Barry, Beverly, Mass. 6 OTHER PUBLICATIONS g sylvallia Electric Products Klasens et a1. Ultraviolet Fluorescence of Some Ternary Si]- [22] Filed: Dec. 23 1968 icates Activated with Lead, Journal of the Electrochemical Society, Vol. 104, No. 2, Feb. 1957, pp. 93- 100 [21] App]. No.: 785,981

Primary ExaminerRobert D. Edmonds s2 U.S. Cl ..313/109, 252/301.4 F oMalley and Meagan [51] Int. Cl ....C09k l/54, HOlj H63 [58] Field of Search ..252/30l.4 F; 313/109 ABSTRACT Divalent europium-activated BaMg Si,O-, phosphors are use- [56] References Cned ful in fluorescent lamps. The phosphors have spectral energy UNITED STATES PATENTS distribution curves which peak at 400 nanometers and which have a very narrow emission band. 2,297,108 9/1942 McKeag et al ..252/30l.4 F

Cassanos ..252/301.4 F

8 Claims, 2 Drawing Figures PATENTEDMMI m2 FIG.

WAVELENGTH IN NANOMETERS ,FIGZ' THOMAS L. BARRY BACKGROUND OF THE INVENTION detrimental. While this formulation represents the approximate composition of the respective compounds in a given phosphor, which can be identified by X-ray diffraction and spectral energy distribution curves, an actual composition may vary from the formula as written without lying outside the scope of the invention.

DESCRIPTION OF PRIOR ART Klasens, Hoekstra, and Cox: J. Electrochem. Soc 104, 93 (1957), conducted an extensive investigation on the fluorescence of the ternary silicate compounds including the systems BaOMgO-SiO SrO-MgOSiO and Ca0- MgOSiO Aside from Pb, they reported trying many of the other usual activators, such as Mn, Tl, Bi, Sb and Sn in the ternary compounds. Although some did show weak fluorescence, 7

none of them led to phosphors of any appreciable efficiency.

SUMMARY OF THE INVENTION Th phps n MszsitOfi Built (F G; 21. 1 1 929 tral energy distribution curve which peaks at 400 nm. and has a very narrow emission band. The width of the emission band at half-height being 25 nm. This combination of a very narrow emission band and the emission peak falling near the vio1et edge of the visible spectrum which is directly visible to the eye is extremely desirable for certain photocopy applications.

Even relatively small additions of calcium (10 mole percent) produce two phases and the emission spectra show a doublet, one band at 400 nm. and a new band at 445nm. When large quantities (up to 30 mole percent calcium) are used, the band at 400 nm. continues to diminish, while the band at 445 nm. increases. At higher calcium concentrations the intensity of both emission bands is reduced.

Strontium, however, may be substituted in quantities less than 30 mole percent for barium in BaMg Si O with a single phase resulting. However, the intensity of the single emission band, which remains at approximately 400 nm., falls off. with increasing strontium concentration. For strontium concentrations of 30 mole percent and beyond, a second emission band at 465 nm. appears, and becomes more pronounced.

Data illustrating the phenomena described above are given in Table 1.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an arc discharge lamp, partially broken away, containing the phosphor in accordance with this invention.

E1G 2 i s an SED curve ofa 13aMg;Si2O1:Eu phosphor of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in FIG. 1 of the drawing, one embodiment of an arc discharge lamp in accordance with this invention com prises a glass envelope 1 and electrodes 2 at each end of the lamp. Within envelope 1 is a'fill which includes mercury. On the inner surface of envelope 1, there is acoating 4 of a barium-magnesium europium activated pyrosilicate phosphor. When an arc is struck between the electrodes, the resultant ultraviolet radiation impinges onto phosphor 4 and excites it to fluorescence. The resultant peak emission is in the 400 nm. region of the spectrum. 7

Starting mixtureswereprepared by dry blending the appropriate proportions of the raw materials in a Mixer/Mill for 15 minutes. The addition of a few glass beads to the raw blend greatly facilitates the mixing process.

The blended mixtures were preflred in alumina boats at 600 C. in air. This firing initiates the decomposition of the alkaline earth carbonates and reaction with the ammonium ior 2637A. intensity excitation of the 400 Composition (nm.) m, band floas gzsirofiEuom 400 100 tm.iaa(38o.1n)MgzSizOrlEuonz 400,445 66 80.78310.2u)Mg2S1z07IEuo,o2 400 82 auhr llmau) g2Si2O1ZEt1u,oz 400,465 30 The prefired samples are then placed in a silica tube which is flushed with nitrogen for 5 minutes and then inserted into the furnace and fired at 1200 C. The gas flow is then adjusted to give a resultant mixture of 4 parts nitrogen to 1 part hydrogen. Firing times of 2 to 12 hours and temperatures ranging between l,100 and 1,300 C. were used at various times, the routine combination being 4 hours at 1,200 C. After firing the silica tube was removed from the furnace and the samples allowed to cool to room temperature in the flowing hydrogen-nitrogen atmosphere.

The ammonium chloride is employed as a flux to enhance the crystallinity of the fired product and any residual chloride is removed after the firing by a water wash.

The following examples are offered as specific .embodiments of my invention.

EXAMPLE I BaM .si o,;Eu%.t4

Material Moles Grams BaCO, 1.00 5.92l 3M co,-M oH ,-3H,o 0.50 5.481 SiO, 2.00 3.605 Eu o 0.02 0.211 NH.C1 0.40 0.642

EXAMPLE 11 03am BB O. m gz z 1 Material Moles Grams BaCO 0.88 5.210 CaCO, 0.10 0.300 3MgCO;,'Mg(OH 3H,O 0.50 5.481 SiO, 2.00 3.605 ElqO; 0.01 0.106 NH CI 0.40 0.642

EXAMPLE III 2+ 210. 1aSr )Mg S1- O :Eu o. 02 Material Moles Grams BaCO, 0.78 4.618

Examples II and IV above do not yield single phase phosphors of the formulas as written. Various changes in the details and materials which have been described herein may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.

lclaim:

'1. A fluorescent material consisting essentially of barium magnesium pyrosilicate activated by europium in sufiicient quantities to produce luminescence, wherein the ratio of barium to magnesium is about one to two.

2. The material according to claim 1 wherein the formula is Ba l 15391 5 5. 32.022 2- 9;

3. The material according to claim 2 wherein strontium is substituted for the barium in quantities less than 30 mole percent.

4. The material according to claim 2 wherein the europium is divalent.

5. A fluorescent lamp including a glass envelope containing mercury having electrodes disposed on the ends thereof and a coating of a fluorescent material consisting essentially of barium magnesium pyrosilicate activated by europium in sufficient quantities to produce luminescence, wherein the ratio of barium to magnesium is about one to two.

6. The lamp according to claim 5 wherein the formula is 7. The lamp according to claim 6 wherein strontium is substituted for the barium in quantities less than 30 mole percent.

8. The lamp according to claim 6 wherein the europium is divalent. 

2. The material according to claim 1 wherein the formula is BaMg2Si2O7:EuEu 005 to
 10. 3. The material according to claim 2 wherein strontium is substituted for the barium in quantities less than 30 mole percent.
 4. The material according to claim 2 wherein the europium is divalent.
 5. A fluorescent lamp including a glass envelope containing mercury having electrodes disposed on the ends thereof and a coating of a fluorescent material consisting essentially of barium magnesium pyrosilicate activated by europium in sufficient quantities to produce luminescence, wherein the ratio of barium to magnesium is about one to two.
 6. The lamp according to claim 5 wherein the formula is BaMg2Si2O7:Eu 005 to
 10. 7. The lamp according to claim 6 wherein strontium is substituted for the barium in quantities less than 30 mole percent.
 8. The lamp according to claim 6 wherein the europium is divalent. 